Spectroscopy refers to determining the nature of a substance by measuring a parameter of energy emitted by the substance. For example, if a laser beam is scattered off of a substance, some of the photons in the scattered beam will have a different wavelength than those in the incident beam. This results from an exchange of energy between the incident photons and the molecules of the substance and is called the Raman Effect. The substance can be identified by measuring how much the wavelength has shifted. The Raman Effect can be enhanced by adsorbing molecules of the substance onto a rough metal surface and then exposing them to the incident laser beam. This technique is referred to as surface-enhanced Raman spectroscopy (SERS). The enhancement factor is so high—as much as 1011—that individual molecules of the substance can be identified. A suitable surface may be prepared by forming tiny projections called nanofingers on a silicon substrate and depositing a thin coating of metal such as gold or silver on the nanofingers. Then, when the nanofingers are exposed to a liquid, the liquid flows between the nanofingers and capillary action causes them to bend toward each other, trapping individual molecules of the liquid. The nanofingers may be thought of as tiny tweezers that hold individual molecules of the liquid up to the laser beam for analysis.